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Why the Alibaba IPO may mark a top for stocks

Chinese e-commerce giant Alibaba is set to raise as much as $24 billion dollars in its initial public offering, valuing the company at some $150 billion, which would make it the biggest IPO ever in terms of both valuation and amount raised. (For the record, Yahoo holds a 22 percent stake in Alibaba, and plans to sell some of that holding in the offering.) But while the massive IPO could be seen as a good sign for markets and for the global economy, some exactly argue that it could actually mark a top to the long bull market in U.S. stocks.

"This is interesting for the market, but I do think it's a little worrisome at some of the levels that we're getting at," said Gina Sanchez of Chantico Global.

It's not that she doesn't think there's enough global liquidity to support the offering. Rather, she thinks the offering indicates that there is far too much global liquidity.

(Read MoreU.S. investors line up in droves to hear Alibaba's pitch)

"There is a lot of money sloshing around, but that is precisely why I believe that we are probably closer to a top then we want to admit," she said.

As more and more money has chased U.S. equities, stock prices have risen. But eventually, that process causes asset prices to run ahead of the fundamentals. Indeed, economist Robert Shiller, for one, has saliently warned that both stocks and bonds look expensive compared with classical measures of value, such as his cyclically adjusted price-to-earnings ratio.

And whether or not the Alibaba IPO indicates a top, it should be no surprise that big IPOs tend to come when investor confidence is high. After all, investment bankers don't look to unveil big offerings at times when most investors are feeling cautious.

"Very few IPOs get done during market troughs; many more make their debuts anywhere from the midpoint of a cycle all the way to the peak," pointed out Nicholas Colas of ConvergEx in a Monday note. "Looking at a history of the top IPOs of all time in U.S. markets," it is clear that "mega-IPOs do tend to happen toward market tops."

Colas notes that the No. 1 biggest IPO to date, for Visa, debuted in March 2008. And the No. 8 biggest, AT&T Wireless, came in April 2000.

Still, not everyone sees a reason to fear.

(Read MoreUS stocks slide on global concerns)

"They say there's no bell that rings at the top, and I wouldn't view the Alibaba IPO as that proverbial bell," said Richard Ross, global technical strategist at Auerbach Grayson. "All year we've been looking for a smoking gun, but the truth when it comes to technology stocks is that there's been no smoke and there's been no gun."

Based on the charts, Ross sees the Nasdaq Composite moving higher all the way up to the level where it topped out in early 2000.

"The trend remains higher," he said. But when the technology index gets up to 4,700, "that record monthly close of one of the biggest bubbles in financial history" will be "staring you right in the face on that chart, and I think it's a warning that you should certainly heed."

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